Minimally invasive techniques and instruments for placement of intraluminal medical devices have been developed over recent years and are frequently used to deliver and deploy an intraluminal medical device at a desired point of treatment. In these techniques, a delivery system is used to carry the intraluminal medical device through a body vessel to the point of treatment. Once the point of treatment is reached, the intraluminal medical device is deployed from the delivery system. The delivery system is subsequently withdrawn from the point of treatment and, ultimately, the body vessel.
A wide variety of intraluminal medical devices that utilize minimally invasive technology has been developed and include stents, stent grafts, occlusion devices, infusion catheters, prosthetic valves, and the like. These devices are frequently used in a variety of treatment procedures. For example, self-expandable stents are used to provide support to various vessels and ducts in the cardiovascular and gastrointestinal systems. Also, prosthetic valves, including prosthetic venous valves, are used to introduce or restore a valving function to a body vessel.
Loading an intraluminal medical device into and deploying the device from a conventional delivery system involves relative movement between the intraluminal medical device and a sheath or other outer tubular member that maintains the device in a compressed state during navigation to the point of treatment. During a loading operation, the intraluminal medical device typically is concentrically oriented with an inner dilator. The dilator and intraluminal medical device are then slidingly inserted into a surrounding sheath. During deployment, relative movement between the dilator and sheath is used until the intraluminal medical device is fully exposed. Typically, the dilator and intraluminal medical device are caused to slide out of the sheath, either by retraction of the sheath, advancement of the dilator, or a combination of both. Eventually, the sheath is no longer able to maintain the device in its compressed state due to the change in relative position(s), and the intraluminal medical device is deployed from the dilator to take its implanted position at the point of treatment within the body vessel.
The friction that occurs between the intraluminal medical device and the inner surface of the surrounding sheath presents an opportunity for damage to occur to the intraluminal medical device. This is particularly true for intraluminal medical devices that include a graft or other material attached to a support frame, such as stent grafts, valve devices with attached leaflets or other valve functional member, tissue graft devices, graft-based occluders, and other devices. If an excessive amount of friction occurs, the attachment between the graft or other material and the support frame can be damaged, which might affect performance of the device. Use of a tacky valve or valve component can also present additional challenges during loading and/or deployment. Damage to the graft or other material itself might also occur.
Friction within delivery systems poses a risk for intraluminal medical devices that require an input of force to achieve intraluminal expansion, such as balloon expandable stents and similar devices, but the problem is of particular concern for self-expandable intraluminal medical devices due to the primary functional role played by the sheath in maintaining these devices in their compressed configurations prior to deployment. With a sheath that provides the constraining force that prevents expansion, friction during relative movement of the dilator or other carrier device and the sheath is a necessary result.
Accordingly, a need exists for a delivery system with an improved release mechanism for expandable intraluminal medical devices.